This invention is directed generally to the field of RF (radio frequency) antenna systems and, more particularly, to a method for isolating the RF output of one antenna from the RF input to another closely-spaced antenna. In radio and television communications systems, it is common to have two or more transmitting antennas in relatively close physical proximity to one another, thereby to minimize the space required for an installation. Frequently, the closely-spaced antennas propagate transmissions which are at or near the same frequency. Thus, the problem arises as to how to isolate the transmission from one antenna from the RF generator powering the other antenna.
The foregoing problem is conventionally addressed by ensuring that adjacent antennas are separated from each other by a distance sufficient to provide about 20 db of isolation. Even though the isolation thus obtained is adequate for most applications, the physical space required for the antenna installation remains undesirably large.
According to another technique which is sometimes used to isolate adjacent antennas, an array of multiple hybrid networks is included between each antenna and its RF source. See, for example, U.S. Pat. No. 4,213,132. Although this technique serves its purpose well, it is desirable to minimize the use of such hybrid networks in order to reduce the cost of antenna installations.
Accordingly, it is a general object of the invention to provide an improved method of installing RF antenna arrays.
It is a more specific object of the invention to provide such a method by which antenna arrays can be more closely spaced to each other without degrading RF isolation between them.
It is another object of the invention to provide the close spacing and isolation referred to above while simultaneously eliminating or, at least, substantially reducing the need for hybrid networks.